This invention relates to a pattern transfer apparatus for transferring onto a wafer a pattern for the manufacture of semiconductor circuit devices such as integrated circuits (ICs), large scaled integrated circuits (LSIs), very large scaled integrated circuits (VLSIs), etc. More particularly, the invention relates to a pattern transfer apparatus for transferring a pattern onto a wafer, having a temperature control system for obtaining alignment between a pattern which has already been transferred onto the wafer and a pattern which is to be transferred onto the wafer.
In general, manufacture of semiconductor devices such as ICs, LSIs, VLSIs, etc. involves repeated pattern projection and transfer steps, for a single wafer, for projecting and transferring different circuit patterns formed on different masks. In order to ensure improved capacities of semiconductor devices and higher throughputs, it is a critical factor to obtain a highly accurate alignment between the pattern of a mask which is to be transferred onto the wafer at the current transfer step with the pattern of another mask which has already been transferred onto the same wafer during the preceding transfer step.
Techniques for obtaining accurate alignment have already been proposed, e.g. as disclosed in Japanese Patent Application Laid-Open Nos. 56-112732 published Sept. 5, 1981, b 57-136325 published Aug. 23, 1982, U.S. Pat. Nos. 4,202,623 issued May 13, 1980, and 4,256,829 issued Mar. 17, 1981. According to these techniques, misalignment between a pattern of a mask which is to be transferred onto a wafer in the current transfer step and a pattern of another mask which has been transferred onto the same wafer in the preceding transfer step is corrected by controlling the temperature of the wafer so that it is thermally expanded or contracted. The temperature of the wafer can be controlled by controlling the temperature of a wafer chuck holding the wafer at the pattern transfer position while maintaining the flatness of the wafer.
The inventor of the present invention has found some inconveniences involved in such techniques.
First, a relatively long stand-by time is required until the temperature of the wafer carried on the wafer chuck reaches a desired temperature. In case of a 5-inch wafer, a stand-by time of approx. 6 sec. is necessary. Such stand-by time is useless and decreases the throughput which is one of the most important properties of the semiconductor circuit manufacturing transfer apparatus. This is a particularly serious problem in the case of a recently developed needlepoint-surface chuck. This type of wafer chuck has a chuck surface which is formed with a multiplicity of needlepoints in order to minimize the area of contact with the wafer to remove any effect of foreign particles adhered on the back surface of the wafer. If such type of wafer chuck is used, it requires a stand-by time which is three or more times as long as that required in ordinary wafer chucks. This results in substantial decrease in the throughput.
Second, when the wafers, each having a temperature which is different from that of the temperature-controlled wafer chuck, are sequentially fed to the wafer chuck, there occurs on the wafer chuck a heat loss of an amount corresponding to the number of the wafers. Usually, in the transfer apparatus, fifty or more wafers per one hour are fed to the wafer chuck. In view of this, it is not so easy to compensate for the heat loss caused by the wafers, to maintain a constant temperature of the wafer chuck.